U.S. Pat. No. 5,250,233 discloses a membrane carburetor having a control chamber delimited by a control membrane and an acceleration pump actuated by a throttle shaft. The acceleration pump includes a pump chamber which is connected via a line to the control chamber. The line opens into the control chamber in the region of fuel openings opening into the intake channel.
The pump chamber of the acceleration pump defines a dead space wherein fuel is drawn in by suction only at pregiven operating conditions or fuel is pumped out. During constant operation in a load state, the volume of the pump chamber remains unchanged and no throughflow of fuel through the pump chamber takes place. In this way, air bubbles can collect in the pump chamber during longer operating times. If these air bubbles are moved into the intake channel during a later acceleration operation, then instability in the running performance of the internal combustion engine and increased exhaust-gas values occur.